Field of the Invention
The invention relates to communication systems and in particular to setting up communication sessions associated with time critical services in communication systems that facilitate packet data communication sessions for users thereof.
Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities such as user equipment and/or other nodes associated with the communication system. The communication may comprise, for example, communication of voice, data, multimedia, and so on. A session may, for example, be a telephone call between users or multi-way conference session, or a communication session between a user equipment and an application server (AS), for example a service provider server. The establishment of these sessions generally enables a user to be provided with various services.
A communication system typically operates in accordance with a given standard or specification which sets out what the various entities associated with the communication system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely, user equipment is provided with a circuit switched service and/or a packet switched service. Communication protocols and/or parameters which shall be used for the connection may also be defined. In other words, a specific set of “rules” on which the communication can be based on needs to be defined to enable communication by means of the system.
Communication systems providing wireless communication for user equipment are known. An example of the wireless systems is the public land mobile network (PLMN). The PLMNs are typically based on cellular technology. In cellular systems, a base transceiver station (BTS) or similar access entity serves wireless user equipment (UE) known also as mobile stations (MS) via a wireless interface between these entities. The communication on the wireless interface between the user equipment and the elements of the communication network can be based on an appropriate communication protocol. The operation of the base station apparatus and other apparatus required for the communication can be controlled by one or several control entities. The various control entities may be interconnected.
One or more gateway nodes may also be provided for connecting the cellular network to other networks e.g. to a public switched telephone network (PSTN) and/or other communication networks such as an IP (Internet Protocol) and/or other packet switched data networks. In such an arrangement the mobile communications network provides an access network enabling a user with a wireless user equipment to access external networks, hosts, or services offered by specific service providers. The access point or gateway node of the mobile communication network then provides further access to an external network or an external host. For example, if the requested service is provided by a service provider located in other network, the service request is routed via the gateway to the service provider. The routing may be based on definitions in the mobile subscriber data stored by a mobile network operator.
An example of the services that may be offered for users such as the subscribers to communication systems are the so-called multimedia services. Some of the communication systems enabled to offer multimedia services are known as Internet Protocol (IP) Multimedia networks. IP Multimedia (IM) functionalities can be provided by means of an IP Multimedia Core Network (CN) subsystem, or briefly IP Multimedia subsystem (IMS). The IMS includes various network entities for the provision of the multimedia services. The IMS services are intended to offer, among other services, IP connections between mobile user equipment.
The third generation partnership project (3GPP) has defined use of the general packet radio service (GPRS) for the provision of the IMS services, and therefore this will be used in the following as an example of a possible backbone communication network enabling the IMS services. The exemplifying general packet radio service (GPRS) operation environment comprises one or more sub-network service areas that are interconnected by a GPRS backbone network. A sub-network comprises a number of packet data service nodes (SN). In this application the service nodes will be referred to as serving GPRS support nodes (SGSN). Each of the SGSNs is connected to at least one mobile communication network, typically to base station systems. The connection is typically by way of radio network controllers (RNC) or other access system controllers such as base stations controllers (BSC) in such a way that packet service can be provided for mobile user equipment via several base stations. The intermediate mobile communication network provides packet-switched data transmission between a support node and mobile user equipment. Different sub-networks are in turn connected to an external data network, e.g. to a public switched data network (PSPDN), via gateway GPRS support nodes (GGSN). The GPRS services thus allow the provision of packet data transmission between mobile data terminals and external data networks.
In such a network, a packet data session is established to carry traffic flows over the network. Such a packet data session is often referred as a packet data protocol (PDP) context. A PDP context may include a radio access bearer provided between the user equipment, the radio network controller and the SGSN, and switched packet data channels provided between the serving GPRS support node and the gateway GPRS support node.
A data communication session between the user equipment and other party would then be carried on the established PDP context. Each PDP context can carry more than one traffic flow, but all traffic flows within one particular PDP context are treated the same way as regards their transmission across the network. The PDP context treatment requirement is based on PDP context treatment attributes associated with the traffic flows, for example quality of service and/or charging attributes.
The Third Generation Partnership Project (3GPP) has also defined a reference architecture for the third generation (3G) core network, which will provide the users of user equipment with access to the multimedia services. This core network is divided into three principal domains. These are the Circuit Switched (CS) domain, the Packet Switched (PS) domain, and the Internet Protocol Multimedia (IM) domain. The latter of these, the IM domain, is for ensuring that multimedia services are adequately managed.
The IM domain supports the Session Initiation Protocol (SIP) as developed by the Internet Engineering Task Force (IETF). Session Initiation Protocol (SIP) is an application-layer control protocol for creating, modifying, and terminating sessions with one or more participants (endpoints). SIP was generally developed to allow for initiating a session between two or more endpoints in the Internet by making these endpoints aware of the session semantics. A user connected to a SIP based communication system may communicate with various entities of the communication system based on standardized SIP messages. User equipment or users that run certain applications on the user equipment are registered with the SIP backbone so that an invitation to a particular session can be correctly delivered to these endpoints. To achieve this, SIP provides a registration mechanism for devices and users, and it applies mechanisms such as location servers and registrars to route the session invitations appropriately. Examples of the possible sessions that may be provided by means of SIP signaling include Internet multimedia conferences, Internet telephone calls, and multimedia distribution.
It is expected that various types of services are to be provided by means of different Application Servers (AS) over IMS systems. Some of these services may be time critical. An example of the time critical services that may be provided over the IMS are the so-called direct voice communication services. A more specific example of these is the Push-to-Talk over Celluar (PoC) service, also known as PTT, Push-To-Talk service. The direct voice communication services arc intended to use the capabilities of the IP Multimedia Subsystem (IMS) for enabling IP connections for mobile user equipment and other parties of the communications, for example other mobile user equipment or entities associated with the network. The service allows a user to engage in immediate communication with one or more other users.
In PoC services communication between a user equipment and a PoC application server occurs on a one-way communications media. A user may open the communications media by simply pushing a tangent key, for example a button on the keyboard of a user equipment. The push to talk button may be a specific button or then any appropriate key of the keyboard. While a user speaks, the other user or users may listen. Bi-directional communication can be offered since all parties of the communications session may similarly communicate voice data with the PoC application server. The turns to speak are requested by pressing the push-to-talk button. The turns may be granted for example on a first come first served basis or based on priorities; hence the name “push to talk.” Users can join the group session they wish to talk to and then press the tangent key to start talking.
In conventional session establishment procedures media capabilities of a user equipment are negotiated during the session set-up procedure. For example, PoC communication between two user equipments (one-to-one communications) or attachment to a PoC group in one-to-many communications requires an SIP session on the control plane. This time alone is fairly long, especially when considering the needs of the time-critical services. The push-to-talk type instant services, on the other hand, are real-time services by their nature. Therefore the user plane connection should be ready with no unnecessary delay after the special tangent or another indication is given to an equipment that the user thereof wants to speak with another party. However, due to the nature of the set-up procedures required for a PDP context, it may take a while until a proper data connection is provided from the request to have one. For example, the PDP context activation together with radio access bearer establishment time in 3GPP release 5 compliant IMS network takes typically more than three seconds.
Because of this, there may be no time for proper end-to-end media capability negotiations, as the media capability negotiations may take too long to be done in the beginning of a session. This may have various disadvantageous effects. For example, a problem is how to provide adequate codec settings from the beginning of a session. If adequate codec information is not available, the bursts may use unnecessary low codec for the type of communications required. Other examples of possible capability information that may need to be negotiated is given in the detailed description.
Therefore it might be advantageous if the capability negotiations could be properly accomplished for the set-up. However, if even more time is required for the set-up, it is possible that users become frustrated and do not wait long enough so that the service they requested could be provided for them. A too long waiting time might also be considered as inadequate from the service level point of view. If a caller has to wait for too long for the start-to-talk-indication, he/she might assume that the request was not successful. The caller may then even repress the tangent. The repressing causes a new SIP session establishment procedure, thus consuming network resources and delaying the session set-up further.